Displays in automotive vehicles are becoming more and more prominent. There is a push for larger displays to become a common feature in cars including entertainment displays for the passenger. The main obstacle preventing this from becoming a reality is privacy: by law in many jurisdictions and otherwise for general safety concerns, a driver must not be able to view moving image content on a display while driving. Accordingly, if a passenger is watching video content on the dashboard display, no light (or no variation of light level) is to be visible from the driver's position. Such result necessitates a strong privacy display, by which image content is visible only from within a specific and limited viewing angle range, and otherwise generally is not visible to a viewer outside of such viewing angle range.
Accordingly, attempts have been made to provide display systems with a strong privacy mode. FIG. 1A is a schematic drawing depicting a liquid crystal device (LCD) configuration 10 as is conventional in the art. FIG. 1B is a schematic drawing depicting an LCD configuration 20 that is representative of an improved privacy display designed by Applicant, as described in Applicant's application Ser. No. 15/981,022 filed on May 16, 2018 (the '022 Application), the contents of which are incorporated herein by reference. In the conventional configuration 10, a backlight 12 emits light 14 to a view angle control film 16, and the light subsequently illuminates a liquid crystal display (LCD) image panel 18. The view angle control film may be a Louvre film as are known in the art. As illustrated by the arrows schematically illustrating the light beams 14, although there is some attenuation of off-axis light by the view angle control film 16, the screening of the off-axis light often is insufficient to provide a full private mode, as some residual off-axis light is still transmitted to the image panel 18 and thus to the viewing side (as indicated by the smaller arrows pointing in the off-axis direction). Accordingly, a strong private mode is not achieved as an image corresponding to the residual off-axis light still may be perceived by an off-axis viewer. Accordingly, the conventional configuration of FIG. 1A results in a privacy mode that in particular does not meet the stringent requirements for automotive applications.
In the LCD device 20 of FIG. 1B that is described in the '022 Application, an additional switchable view angle control LCD 22 is incorporated into the device. The switchable view angle control LCD 22 may be a switchable scattering LCD that can be electrically switched between a first mode (Mode 1 in FIG. 1B) and a second mode (Mode 2 in FIG. 1B). In the first mode (Mode 1), the switchable view angle control LCD 22 performs a view angle restriction function without scattering light to provide a narrow angle viewing or private mode. Comparing Mode 1 to the conventional configuration, the off-axis light that might not be screened out by the view angle control film 16 is now blocked by the switchable view angle control LCD 22. In this manner, an enhanced privacy mode is achieved as compared to conventional configurations. In the second mode (Mode 2), the switchable view angle control LCD 22 operates to perform a light scattering function to achieve a wide angle viewing or public mode.
Accordingly, the configuration of the '022 Application of FIG. 1B addresses the automotive industry need for a display system that can switch between a strong private mode and a public mode. As described in the '022 Application, one way of achieving switchable privacy is to have a switchable scatterer positioned above a privacy optic such as the above-mentioned Louvre film. For example, the '022 Application describes a hydrodynamic hybrid-aligned nematic (HHAN) cell that, in a first mode, enhances the privacy of the display device, and in a second mode, scatters the previously collimated light off-axis to provide the public mode. One drawback of this system, however, is that the light efficiency is low and the public mode can appear dim because a Louvre film generally has a low light efficiency, transmitting only about 35% of the light from a backlight. When the HHAN cell is placed in the scattering mode, the already low level of collimated light is scattered out to wider angles, which can result in a dim public mode.